Motion transmitting remote control assemblies are typically employed to control a device by transmitting tension or compression in a curved path by means of a flexible core element. Remote control assemblies of this type include a casing surrounding a motion transmitting core element which is moved back and forth in the casing to remotely control or position an element to which the core element is attached. Exemplary applications to which the instant invention pertains includes high performance military aircraft component control such as primary flight controls and jet engine throttle control. Accordingly, it will be appreciated that during active operation the remote control assembly is required to transmit high load forces over long distances, and such must be accomplished with minimal core element backlash. Backlash, more particularly, is the lack of responsiveness in a remote control assembly resulting from a loose fit (typically an excessive running clearance) between the core element and its casing or, in the case of the instant invention, between the core element and the roller assembly. This lack of responsiveness causes an excessive amount of input motion on the core element before output motion is realized. In critical applications, such as high performance military aircraft, the lack of responsiveness resulting from excessive backlash is highly undesired.
U.S. Pat. No. 3,438,280 to McCabe, issued Apr. 15, 1969 and assigned to the assignee of the subject invention, discloses a remote control assembly of the type described above. In this example, the casing is fabricated by winding a plurality of long lay wires in helical turns and encasing them in plastic to form an inner passage through which the core element is positioned. Casings fabricated after this construction can have a significant drawback which is clearly recognized by McCabe. That drawback is that the plastic encasing the inner lay wires is not sufficient to restrain the lay wires from unwinding during high loading on the core element, such high loading as frequently occurs in high performance military aircraft. The McCabe reference recognized that the casing is not capable of restraining the side loads of the core element during high load applications, and accordingly constructed two races on opposite sides of the core element to act as tension carrying members. This was accomplished by locking, or restraining, both ends of the races relative to the casing. It will be readily appreciated by those skilled in the art that one or both of the races must be moveable during installation to retain flexibility of the casing and allow the casing to be routed through curved sections between its ends. Therefore, locking of the races occurs after installation is complete.
However, the McCabe construction proved, over time, to still be inadequate to restrain backlash because under high loading conditions, the fixed races would still impart side loads against the rather weak casing, which in turn flexed and bulged in isolated sections to result in increased backlash.
Therefore, over the years, the industry has developed more sophisticated constructions which do not rely upon the races for resisting side loading of the core element. As a result, structurally stable casings have been constructed which do not deform under high loading conditions. These flexible casings are formed by at least one inner lay wire wounded in helical turns at a predetermined pitch to form a tubular inner passage, and at least one outer support wire wound in helical turns tightly about the exterior of the inner lay wire at a pitch different than the predetermined pitch of the inner lay wire to restrain deformation of the inner lay wire from slide loads applied against the inner passage by the core element. Thus, because the casings are now of sufficiently sound construction to resist all foreseeable side loading, even during operation of high performance military aircraft, the races inside the casing are left preputially moveable within the casing, i.e., unlocked, to preserve the flexibility of the casing. That is, there is presently perceived no need to lock the races relative to the casing because the casing itself is sufficiently strong enough to resist all foreseeable side loading by the core element. An example of a typical prior art remote control assembly having an improved casing construction is shown in U.S. Pat. No. 5,105,678 to Adelman et al, issued Apr. 21, 1992 and assigned to the assignee of the subject invention.
Thus, the prior art has progressed to a state where additional backlash is not introduced into the system as a result of high loading applied during operation. However, the inherent backlash resulting from the running clearance between the roller assemblies and the core element still results in a certain amount of backlash which the prior art is not capable of reducing or eliminating.